208 research outputs found
Distributing Secret Keys with Quantum Continuous Variables: Principle, Security and Implementations
The ability to distribute secret keys between two parties with
information-theoretic security, that is, regardless of the capacities of a
malevolent eavesdropper, is one of the most celebrated results in the field of
quantum information processing and communication. Indeed, quantum key
distribution illustrates the power of encoding information on the quantum
properties of light and has far reaching implications in high-security
applications. Today, quantum key distribution systems operate in real-world
conditions and are commercially available. As with most quantum information
protocols, quantum key distribution was first designed for qubits, the
individual quanta of information. However, the use of quantum continuous
variables for this task presents important advantages with respect to qubit
based protocols, in particular from a practical point of view, since it allows
for simple implementations that require only standard telecommunication
technology. In this review article, we describe the principle of
continuous-variable quantum key distribution, focusing in particular on
protocols based on coherent states. We discuss the security of these protocols
and report on the state-of-the-art in experimental implementations, including
the issue of side-channel attacks. We conclude with promising perspectives in
this research field.Comment: 21 pages, 2 figures, 1 tabl
Continuous-variable quantum authentication of physical unclonable keys
We propose a scheme for authentication of physical keys that are materialized
by optical multiple-scattering media. The authentication relies on the optical
response of the key when probed by randomly selected coherent states of light,
and the use of standard wavefront-shaping techniques that direct the scattered
photons coherently to a specific target mode at the output. The quadratures of
the electromagnetic field of the scattered light at the target mode are
analysed using a homodyne detection scheme, and the acceptance or rejection of
the key is decided upon the outcomes of the measurements. The proposed scheme
can be implemented with current technology and offers collision resistance and
robustness against key cloning.Comment: 15 pages, 7 figure
Quantum superiority for verifying NP-complete problems with linear optics
Demonstrating quantum superiority for some computational task will be a
milestone for quantum technologies and would show that computational advantages
are possible not only with a universal quantum computer but with simpler
physical devices. Linear optics is such a simpler but powerful platform where
classically-hard information processing tasks, such as Boson Sampling, can be
in principle implemented. In this work, we study a fundamentally different type
of computational task to achieve quantum superiority using linear optics,
namely the task of verifying NP-complete problems. We focus on a protocol by
Aaronson et al. (2008) that uses quantum proofs for verification. We show that
the proof states can be implemented in terms of a single photon in an equal
superposition over many optical modes. Similarly, the tests can be performed
using linear-optical transformations consisting of a few operations: a global
permutation of all modes, simple interferometers acting on at most four modes,
and measurement using single-photon detectors. We also show that the protocol
can tolerate experimental imperfections.Comment: 10 pages, 6 figures, minor corrections, results unchange
Asymptotic security of continuous-variable quantum key distribution with a discrete modulation
We establish a lower bound on the asymptotic secret key rate of
continuous-variable quantum key distribution with a discrete modulation of
coherent states. The bound is valid against collective attacks and is obtained
by formulating the problem as a semidefinite program. We illustrate our general
approach with the quadrature phase-shift keying (QPSK) modulation scheme and
show that distances over 100 km are achievable for realistic values of noise.
We also discuss the application to more complex quadrature amplitude
modulations (QAM) schemes. This work is a major step towards establishing the
full security of continuous-variable protocols with a discrete modulation in
the finite-size regime and opens the way to large-scale deployment of these
protocols for quantum key distribution.Comment: 11 pages, 5 figures; v2: added discussion of more general quadrature
amplitude modulation schemes, v3: close to published versio
Experimental wavelength division multiplexed photon pair distribution
We have experimentally implemented the distribution of photon pairs produced
by spontaneous parametric down conversion through telecom dense wavelength
division multiplexing filters. Using the measured counts and coincidences
between symmetric channels, we evaluate the maximum fringe visibility that can
be obtained with polarization entangled photons and compare different filter
technologies.Comment: 3 pages, 4 figures, submitted to Optics Letter
100 km secure differential phase shift quantum key distribution with low jitter up-conversion detectors
We present a quantum key distribution experiment in which keys that were
secure against all individual eavesdropping attacks allowed by quantum
mechanics were distributed over 100 km of optical fiber. We implemented the
differential phase shift quantum key distribution protocol and used low timing
jitter 1.55 um single-photon detectors based on frequency up-conversion in
periodically poled lithium niobate waveguides and silicon avalanche
photodiodes. Based on the security analysis of the protocol against general
individual attacks, we generated secure keys at a practical rate of 166 bit/s
over 100 km of fiber. The use of the low jitter detectors also increased the
sifted key generation rate to 2 Mbit/s over 10 km of fiber.Comment: 10 pages, 5 figure
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